1. Field of the Invention
This invention relates to concrete products, and more particularly to a structural insulative lightweight concrete.
2. Description of the Prior Art
Lightweight concrete compositions per se are known in the art. Frequently this type of product is produced by formulating a concrete mix with lightweight aggregates. Among the lightweight aggregate materials which have been employed in the prior art to produce lightweight concretes are expanded shale, pumice, volcanic tuffs, sintered diatomite, blast furnace slag, sintered flyash, perlite, and vermiculite.
The lightweight concretes of the prior art employing these aggregate materials, however, have not achieved both high strength and high thermal resistance. In general, those materials possessing suitable structural strength (i.e., over 1000 psi code or 2500 psi design) have low thermal resistance (R) values, i.e., in the range of less than 1. (Hard rock concrete has an R value of 0.08.) Those lightweight concretes possessing higher R values such as perlite or vermiculite-containing materials (R=1 to 2) do not possess sufficient strength for structural use.
Applicant is aware of no lightweight concrete which has sufficient strength for structural applications and yet has a high enough thermal resistance to be a significantly insulating material. Thus, at a time when energy resources are becoming increasingly scarce, a structural lightweight concrete that is also significant in its insulative properties would be a welcome advance.